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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/userspace-api/media/cec/cec-intro.rst | |
parent | Initial commit. (diff) | |
download | linux-5d1646d90e1f2cceb9f0828f4b28318cd0ec7744.tar.xz linux-5d1646d90e1f2cceb9f0828f4b28318cd0ec7744.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/userspace-api/media/cec/cec-intro.rst')
-rw-r--r-- | Documentation/userspace-api/media/cec/cec-intro.rst | 42 |
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diff --git a/Documentation/userspace-api/media/cec/cec-intro.rst b/Documentation/userspace-api/media/cec/cec-intro.rst new file mode 100644 index 000000000..1884ea090 --- /dev/null +++ b/Documentation/userspace-api/media/cec/cec-intro.rst @@ -0,0 +1,42 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later + +.. _cec-intro: + +Introduction +============ + +HDMI connectors provide a single pin for use by the Consumer Electronics +Control protocol. This protocol allows different devices connected by an +HDMI cable to communicate. The protocol for CEC version 1.4 is defined +in supplements 1 (CEC) and 2 (HEAC or HDMI Ethernet and Audio Return +Channel) of the HDMI 1.4a (:ref:`hdmi`) specification and the +extensions added to CEC version 2.0 are defined in chapter 11 of the +HDMI 2.0 (:ref:`hdmi2`) specification. + +The bitrate is very slow (effectively no more than 36 bytes per second) +and is based on the ancient AV.link protocol used in old SCART +connectors. The protocol closely resembles a crazy Rube Goldberg +contraption and is an unholy mix of low and high level messages. Some +messages, especially those part of the HEAC protocol layered on top of +CEC, need to be handled by the kernel, others can be handled either by +the kernel or by userspace. + +In addition, CEC can be implemented in HDMI receivers, transmitters and +in USB devices that have an HDMI input and an HDMI output and that +control just the CEC pin. + +Drivers that support CEC will create a CEC device node (/dev/cecX) to +give userspace access to the CEC adapter. The +:ref:`CEC_ADAP_G_CAPS` ioctl will tell userspace what it is allowed to do. + +In order to check the support and test it, it is suggested to download +the `v4l-utils <https://git.linuxtv.org/v4l-utils.git/>`_ package. It +provides three tools to handle CEC: + +- cec-ctl: the Swiss army knife of CEC. Allows you to configure, transmit + and monitor CEC messages. + +- cec-compliance: does a CEC compliance test of a remote CEC device to + determine how compliant the CEC implementation is. + +- cec-follower: emulates a CEC follower. |